The present disclosure is related to downhole tools and, more particularly, to protecting downhole tools during wellbore cementing operations.
In the oil and gas industry, wellbores are drilled into the Earth's surface in order to access underground reservoirs for the extraction of hydrocarbons. Once a wellbore is drilled, it is often lined with casing or a string of casing lengths, and the casing is then secured into place using cement. In one cementing technique, a cement composition is pumped through the interior of the casing and allowed to flow back toward the surface via the annulus defined between the wellbore wall and the casing. The cement composition within the annulus is then allowed to cure, forming a hardened mass in the annulus. In another cementing technique, commonly referred to as reverse-circulation cementing, the cement composition is pumped through the annulus to the bottom of the wellbore and then back toward the surface via the interior of the casing. Once the cement composition cures within the annulus to form a hardened mass, the casing serves to stabilize the walls of the surrounding subterranean formation to prevent any potential caving into the wellbore. The casing also isolates the various surrounding subterranean formations by preventing the flow or cross-flow of formation fluids via the annulus. The casing further provides a surface to secure pressure control equipment and downhole production equipment, such as a drilling blowout preventer (BOP) or a production packer.
In some downhole applications, one or more downhole tools may be run downhole with the casing and permanently installed therewith, meaning that the downhole tools are meant to remain within the casing throughout the life of the well. Such downhole tools are typically arranged on the exterior of a casing mandrel coupled to the casing string at a predetermined location in the wellbore. An example of such a downhole tool is a chemical injector, which may remain in fluid communication with a surface location by being ported to the interior of the casing at a tool port. Various treatment fluids and/or chemicals may be conveyed from the surface to the chemical injector to be injected into the casing at the tool port for various purposes. Another exemplary downhole tool is a gauge mandrel that includes various gauges and/or sensors that are ported to the interior of the casing at a tool port. Such gauges/sensors may monitor the fluids circulating in the casing and report real-time fluid parameters (i.e., temperature, pressure, etc.) to a surface location (e.g., via wired or wireless communication).
While cementing the casing within the wellbore, however, the cement composition and/or other wellbore debris may obstruct and otherwise occlude the tool port that provides fluid communication between the downhole tool and the interior of the casing. If the tool port is obstructed, then operation of the downhole tool will likely be frustrated.
To prevent the influx of the cement composition or other wellbore debris into the tool port, a burst disk may be utilized, which is typically arranged within the tool port. Following placement of the cement composition, the casing may be pressurized to rupture the burst disk and thereby initiate fluid communication between the permanent downhole tool and the interior of the casing. The burst disk, however, is susceptible to failure during the cementing operation and can otherwise develop premature leaks. As a result, the burst disk is often unable to rupture in response to the increased fluid pressure within the casing, thereby rendering the downhole tool inoperable for its intended purpose.